In order to provide high time constants in RC circuits, it is desirable to fabricate components with values of the resistance R and capacitance C as high as possible. With the trend toward smaller line widths, it becomes increasingly difficult to maintain a high value capacitance because capacitance is proportional to the area of the plates and inversely proportional to their separation.
European patent no. 0,188,946 discloses a method of forming capacitors, in which a sandwich structure is deposited in grooves approximately 5 microns deeps formed in the substrate. While this technique can increase the capacitance relative to a conventional horizontal capacitor, it is does not provide sufficient capacitance for modern devices, for example, using 0.8 micron technology. Also, the method described in this patent does not lend itself to being conveniently integrated into a standard fabrication process.
Co-pending British application no. 9801322.0 describes method of forming capacitors in an integrated circuit wherein a conformal sandwich structure extends into holes formed in insulating layer. The preferred structure employs TiN electrodes with a TiO.sub.2 dielectric layer. In this process, it was envisaged that the TiO.sub.2 dielectric layer would be formed in the same chamber as the electrode layers. While the structure has highly desirable properties, in large part due to the convenience of working with the same metal and the high dielectric constant of TiO.sub.2, the fabrication of the TiO.sub.2 layer involves in the same chamber involves certain practical difficulties due to the difficulty of handling oxygen in cryopumps. If adequate precautions are not taken, there is a risk of explosion.
Furthermore, in order to keep the manufacturing costs within economic bounds, it is important to limit the number of additional masking steps required to fabricate the device. Each extra masking step adds to the complexity and thus cost of manufacture.
An object of the invention is to provide a method of making low cost, high value capacitors in integrated circuits.